Self-locking threaded fastener

ABSTRACT

A reusable self-locking threaded fastener is provided having a patch of nylon or like thermoplastic material bonded to several convolutions of the unmodified thread surfaces and gradually merging at its boundary edge portions into the thread surfaces, the nylon patch being melted and fused and solidified without work-shaping pressures and containing from about 0.1 percent to about 5 percent by weight of molybdenum disulfide; a reusable self-sealing and self-locking fastener is provided in which the unmodified nylon patch has a circumferential extent of about 200* to about 300*; by adding to the nylon patch molybdenum disulfide the circumferential extent may be 360*; a method of forming the self-sealing and self-locking fasteners is provided wherein the heated fastener has the nylon in powdered form, and if desired the molybdenum disulfide mixed therein, dropped thereonto while the fastener rotates about its longitudinal axis to melt and hold a quantity of the nylon thereon, after which the fastener may be heated to the fusion temperature of the nylon to further melt the patch; further a primer coating of epoxy resin is provided between the patch and the fastener; the resultant fastener can be reused a minumum of five times and still retain the desired self-locking and self-sealing characteristics thereof.

United States Patent [72] lnventors Charles C. Faroni Summit, N.J.; John S. Humphrey, Jr., Johnson City, N.Y. [21 Appl. No. 618,263 [22] Filed Feb. 6, 1967 [45] Patented Mar. 9, 1971 [73] Assignee Amerace Esna Corporation New York, N.Y.

[54] SELF-LOCKING THREADED FASTENER 19 Claims, 27 Drawing Figs. [52] U.S. Cl 151/7, 1 17/ 128.4, 156/320, 156/330, 264/271 [51] Int. Cl. F1611 39/34 [50] Field olSearch ..151/7, 14.5;

85/1 (C); 10/10, 86 (A); 264/271, 274, 269, 267; 117/1284, 75, 37 (LX), 161 (P), 97; 156/330, 293, 320-22; 285/( Mastic Digest) [56] References Cited UNITED STATES PATENTS 2,939,805 6/1960 Johnson 85/ 1C 2,989,107 6/1961 'James et a1. 151/7 3,002,770 10/1961 Chestnut et a1. 85/ 1C 3,061,455 10/1962 Anthony 15 H7 3,093,177 6/1963 Villo l5l/7 4 3,264,131 8/1966 Nagel 117/75 3,294,l39 12/1966 Preziosi Primary Examiner-Ramon S. Britts Attorney-Prangley, Clayton, Mullin, Dithmar and Vogel ABSTRACT: A reusable self-locking threaded fastener is provided having a patch of nylon or like thermoplastic material bonded to several convolutions of the unmodified thread surfaces and gradually merging at its boundary edge portions into the thread surfaces, the nylon patch being melted and fused and solidified without work-shaping pressures and containing from about 0.1 percent to about 5 percent by weight of molybdenum disulfide; a reusable self-sealing and self-locking fastener is provided in which the unmodified nylon patch has a circumferential extent of about 200 to about 300"; by adding to the nylon patch molybdenum disulfide the circumferential extent may be 360; a method of forming the self-sealing and self-locking fasteners is provided wherein the heated fastener has the nylon in powdered form, and if desired the molybdenum disulfide mixed therein, dropped thereonto while the fastener rotates about its longitudinal axis to melt and hold a quantity of the nylon thereon, after which the fastener may be heated to the fusion temperature of the nylon to further melt the patch; further a primer coating of epoxy resin is provided between the patch and the fastener; the resultant fastener can be reused a minumum of five times and still retain the desired self-locking and self-sealing characteristics thereof.

PATENTEDHAR 9191: 3,568,746

SHEET 1 OF 7 v IO By I Inventors CHARLES C. FARONI JOHN S. HUMPHREYJ PATENTEU m 9 1971 saw a DP 7 WT] 2 F|G.11/

PATENTEDHAR 9|97| 3568746 SHEET 5 OF 7 IELFJLIIHIG THREADED FASTENER The present invention is directed to reusable self-locking threaded fasteners, and particularly to such fasteners that are also self-sealing in character, andto methods of making the same, and is an improvement on the fasteners and methods disclosed in US. 8. Pat. No. 3,294,139 granted Dec. 27, 1966 to .Ioseph R. Preziozi.

It is an important object of the present invention to provide an improved reusable self-locking threaded fastener wherein the self-locking characteristic is provided a method for mak ing by a patch of solid thermoplastic material bonded to a plurality of convolutions of the unmodified thread surfaces, the fastener being capable of many applications and removals without losing the self-locking characteristics thereof. I

In connection with the foregoing object, it is another object of the invention to provide a method for making a self-locking threaded fastener of the type set forth wherein the patch is formed of thermoplastic material melted and fused and solidified without work-shaping pressures, the thermoplastic material containing from about 0.1 percent by weight to abou percent by weight of molybdenum disulfide.

Another object of the invention'is to provide a method for making a self-locking threaded fastener of the type set forth wherein a primer coating ofsynthetic organic resin material is disposed between the surface of the thread and the patch to provide improved adherence therebetween, the preferred resin material being an epoxy resin.

Yet another object of the invention is to provide a method for making a self-locking fastener of the type set forth which is also self-sealing, the patch having a circumferential extent in the range of from about 200 to about 300, a primer coating of a resin material such as an epoxy resin preferably being provided between the patch and the fastener.

In connection with the foregoing object, another object of the invention is to provide a method for making a self-locking and self-sealing fastener that is externally threaded and is provided with a patch of thermoplastic material having a circumferential extent of at least about 200", the thermoplastic material containing from about 0.1 percent by weight to about 5 percent by weight of molybdenum disulfide, such fasteners being capable of having 360 circumferential extent of the patch without loss of the patch during the application of the fastener inits intended use.

A further object of the invention is to provide an improved method of making reusable self-locking and self-sealing screws of the type set forth, the method including the steps of heating the screw to a temperature above the melting temperature of the thermoplastic material used as a patch thereon, depositing upon a selected area the thread of the heated screw a quantity of the thermoplastic material in fine powdered form while rotating the screw around its longitudinal axis, at least a portion of the thermoplastic material being melted by the heat of the screw and adhering thereto and to the thermoplastic material, and thereafter cooling the thermoplastic material to a temperature below the flow point thereof to provide a unitary cohesive body of solid thermoplastic material bonded to the thread.

Further features of the invention pertain to the steps of the methods whereby the above-outlined and additional operating features thereof are attained.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings, in which:

FIG. i is a front elevational view of a pressure apparatus incorporat ng therein a self-locking and self-sealing screw made in accordance with and embodying the principles of the present invention;

FIG. 2 is an enlarged view in vertical section through the apparatus of FIG. 1 along the line 2-2 thereof and further illustrating the screw of the present invention;

FIG. 3 is a perspective view of the self-locking and self-sealing screw of the present invention illustrated in FIGS. 1 and 2;

FIG. d is a plan view on an enlarged scale of the screw of FIG. 3}

FIG. 5 is a partial side elevational view along the lines 5-5 of FIG.

FIG. 6 is a fragmentary longitudinal cross-sectional view along the line 6-6 of FIG. 5;

FIG. 7 is a transverse cross-sectional view along the line 7-7 of FIG. 6;

FIG. 8 is a transverse cross-sectional view along the line 8-8 of FIG. 6; I

FIGS. 9 and 10 are schematic representations of the method and apparatus for making the screw of FIGS. I to 8, inclusive;

FIG. 11 is a view in vertical section'through a valve incorporating therein a second form of threaded fastener made in accordance with and embodying the principles of the present invention;

FIG. 12 is a view in longitudinal section through the fastener of FIG. 11 along the line 12-12 of FIG. 13;

FIG. 13 is an elevational view of the fastener of FIG. 11 on a slightly enlarged scale;

FIG. 14 is a view in transverse cross section along the line 14-14 of FIG. 13;

FIG. 15 is a view in transverse cross section along the line 15-15 ofFlG. 13;

FIG. 16 is a perspective view of a third embodiment of. a threaded fastener made in accordance with and embodying the principles of the present invention;

FIG. 17 is a plan view on an enlarged scale of the fastener of FIG. 16;

FIG. 18 is a fragmentary cross-sectional view along the lines 18-18 ofFIG. 17;

FIG. 19 is a transverse cross-sectional view along the lines 19-19 ofFIG. 18;

FIG. 20 is a transverse cross-sectional view along the line ZII-ZII of FIG. 18; 1

FIG. 21 is a perspective view of a fourth embodiment of a threaded fastener in the form of a nut made in accordance with and embodying the principles of the present invention;

FIG. 22 is a longitudinal cross section on an enlarged scale along the line 22-22 of FIG. 2i;

FIG. 23 is a longitudinal cross section on an enlarged scale along the line 23-23 of FIG. 21;

FIG. 24 is a partial transverse cross section along the line 24-24 of FIG. 22;

FIG. 25 is a fragmentary transverse cross section along the line 25-25 of FIG. 22;

FIG. 26 is a fragmentary transverse cross section along the line 26-26 of FIG. 22; and

FIG. 27 is a view in longitudinal section illustrating an engagement between the nut of FIGS. 21 to 26 and an associated screw.

There is illustrated in FIG. 1 of the drawings a pressure vessel 101} in which the improved screw of the present invention is particularly useful, the screw 111 being both selflocking and self-sealing in character and also reusable. The pressure vessel 1% more specifically includes an inlet pipe 1411 and an outlet pipe 102, the outlet pipe m2 having an outwardly directed flange 1% which bears against a gasket 104 disposed between the flange 103 and the vessel IIII), a plurality of the improved screws 111) being provided to connect the flange 1113 to the vessel 1%. More specifically, each screw 11d extends through aligned openings 1115 and 1% in the flange 1413 and the gasket 1%, respectively, and into a threaded opening 107 in the vessel 104), the threaded opening 107 communicating with the interior of the vessel 100, and therefore being exposed to the pressures therein. Not only must the screws 11.0 hold the flange 1193 in the operative position, but the screws 110 in accordance with the present invention actually seal the threaded openings 107 in the vessel 1% that receive the shanks of the screws 1 it).

Referring now more particularly to FIGS. 3 to 3 of the drawings, the details of construction of one of the screws 11% will be described. The screw 110 includes an elongated shank 111 provided at one end thereof with an enlarged head 112 that provides engagement surfaces for a tool. Formed along the greater portion of the length of the shank 111 is a continuous helical thread 113, the thread 113 being of standard form and shape as illustrated in the drawings. Disposed upon and covering the entire outer surface of the screw 110 is a coating of primer material, preferably an epoxy resin, and disposed on a portion of the threads 113 is a patch 120 of thermoplastic material formed without application of work-shaping or molding pressures. The patch 120 more specifically is a resiliently deformable plastic patch of limited axial extent and substantial circumferential extent. As illustrated, the patch 120 covers approximately five convolutions of the thread 113 out of a total of approximately twelve convolutions, and referring to FIG. 8, it will be seen that the circumferential extent of the patch 1.20 at its point of greatest circumferential extent is approximately 270; more particularly, the patch 120 has a pair of ends 121 that are generally rounded in shape and a pair of sides 122 that extend circumferentially around the greater portion of the diameter of the associated convolutions of the thread 113. The boundary edge portions of the patch 120 gradually merge into the surfaces of an associated convolution of the thread 113, and in particular the end edges 123 associated with the ends 121 merge into the associated surfaces of the convolutions of the thread 113 as do the side edges 124 associated with the sides 122. Finally, the inner surface 128 of the patch 120 conforms generally to the outer surface of the thread 113 in the associated area thereof and is tightly bonded thereto, the epoxy coating 115 assisting in this bond, and the outer surface 129 of the patch 120 only roughly corresponds to the shape of the associated convolutions of the thread 113, see FIGS. 4 and 5, for example.

In order to reduce the stripping and shearing components of the forces exerted by the thread of a mating threaded opening during the insertion of the screw 110 thereinto, and in order to provide the desired initial locking torque, as well as to provide satisfactory locking torques over a number of reuses of the screw 110, the thickness and configuration of the plastic patch 120 is that illustrated in the drawings, FIGS. 2 to 8. The main portion of the patch 120 has a generally uniform thickness, chosen for the primary purpose of obtaining the desired final locking torque. The thickness of the plastic patch gradually diminishes circumferentially from the main body portion to the longitudinally boundary edges 123 and also gradually diminishes longitudinally to the boundary edges 124. Thus the boundary edges 123 and 124 will be the first parts of the plastic patch 120 to engage a complementary internal thread as the screw 110 is moved into the engaged position. The gradual increase in the thickness of the plastic patch throughout the edge portions 123 and 124, and in the thread tightening direction, serves to effect a gradual engagement of the plastic patch 120 with the oncoming complementary thread such as the thread 108 about the opening 107 in the vessel 100, and gradually builds up the deforming forces to a maximum at the main body portion of the patch 120.

Since the forces, or components thereof, which tend to peel the plastic patch 120 from the thread 113 are those extending in the direction of rotation of the'screw when tightening the same, the gradual engagement of the oncoming internal thread 108 assures a gradual deformation of the patch 120 and a gradual increase in the deforming forces applied to the patch 120 so as to build up to a maximum as the thickness of the plastic patch 120 increases, and the maximum forces are applied to a location remote from the edges 123 and 124 of the patch 1.20 and are ineffectual to effect a peeling of the patch.

The plastic patch 120 is deformable when the normal screw tightening pressures are applied thereto and serves to mate against the associated thread 108 and completely to seal the space between the thread 108 and the thread 113, the deformation of the patch 120 being fundamentally responsible for providing the complete sealing between the threads 103 and 113 despite the fact that the patch 1.20 has a circumferential extent of only 270.

The plastic patch 120 is, as shown, a unitary cohesive body with its inner metal contacting surface 123 contiguous with the thread defining surfaces of the thread 113 from the root surfaces thereof to and over the crest surfaces thereof. It is noted that the longitudinal boundary edges of the sides 122 taper longitudinally from a central portion of greater angular or circumferential extent to the edges 124. This longitudinal tapering of the body 120 further enhances the gradual buildup of the plastic deforming forces, thereby precluding peeling of the patch 120 from the thread 113. Thus the deforming forces are spread over greater longitudinal and circumferential distances to increase the area of the unitary plastic patch 120 over which such forces act and to decrease the concentration of the building forces which tend to tear the plastic patch 120 from the screw thread 113.

It should be noted that the leading edge 122 of the plastic patch 120 terminates at a point spaced from the leading end of the screw thread 113 by a distance of at least one full thread convolution to assure proper mating with an associated internal thread prior to the engagement of the latter with the plastic patch 120. The advantages of a gradual engagement between the plastic patch 120 and the associated internal thread of a mating element are further realized by decreasing the thickness or depth of the plastic patch 120 from a maximum at the central portion to a minimum at the ends 121 and the sides 122, see FIGS. 4 through 8.

In accordance with the present invention, the patch 120 must provide both laterally directed wedging forces to lock the screw with respect to the thread of a mating element and sealing forces to seal the space between the thread 113 and the associated thread, such as thread 108 in FIG. 2, the resultant seal serving to prevent both flow along the helical thread path and an axial type of cascade flow along those portions of the thread 113 not carrying a portion of the patch 120. The patch 120 will be both self-locking and self-sealing as described above if it has an appreciable longitudinal extent and a circumferential extent in the range from about 200 to about 300". It has been found that the patch 129 is deformed circumferentially during engagement with a mating threaded element to provide a good seal against liquids, such as oil and water, and against gases, such as air; the seal is provided whether or not the screw is seated or loaded.

The assembly shown in FIG. 2 wherein the plastic patch has a circumferential extent of 270 (see FIG. 8) seals tightly with no leaks against a pressure of I00 p.s.i. of air even when the entire assembly is at 212 F. If the circumferential extent of the plastic patch 120 is less than 200", the plastic patch 120 provides satisfactory locking action but does not seal against axial flow of liquids and gases. If the circumferential extent of the plastic patch is greater than 300, the shear or frictional drag forces exerted by the mating threads, such as the mating threads 108 in FIG. 2, serve to tear and rip and irregularly distort the plastic patch 120 because there is no available space into which the material of the plastic patch 120 can flow under load. As a result, the locking torque is very high for the first use of the screw, and the first removal of the screw from the mating element tears the plastic patch 120 from the thread 113, thus rendering the screw unfit for reuse.

The plastic patch 120 may be readily formed in the configuration described by depositing the plastic material in the form of a fine powder which is subsequently melted and cooled to produce, by the action of gravity and as determined by the surface tension of the melted plastic, a continuous, integral, cohesive patch of plastic material adhered to the thread defining surfaces of the screw. The configuration of the patch is controlled by controlling the distribution, or depositing, of the plastic powder over the screw thread.

FIGS. 9 and Ml schematically illustrate the improved method and apparatus of the present invention for depositing fine plastic powder over a limited area of the screw thread surface. Referring to FIG. 9, the resin or plastic applying apparatus includes a screw holder 151 arranged to receive and to hold the head 112 of a screw 110 with the longitudinal axis of the screw lib disposed substantially horizontal. The

holder 3 .51 is further mounted (by means not shown) to rotate about an axis coaxial with the longitudinal axis of the screw lltl, a pulley 152 and a driving belt E53 therefor being provided for the holder l5l to cause rotation thereof as described. As a result, the screw lib can be rotated about its longitudinal axis by means of the holder lfill engaging the head Ill2 only, and while the longitudinalv axis of the screw is dispomd generally horizontal.

Disposed above the thread lid on the screw Jill) positioned in the holder lfil is a hopper ll5 for the powdered plastic, the hopper 155 being generally in the form of an inverted cone having an annular outlet E56 disposed above an in alignment with a predetermined portion of the thread 113 to direct a stream l57 of powdered plastic thereon. The shape of the outlet i156, assures that maximum amounts of the powdered plastic are deposited in the center of the area of the thread lld therebelow and lesser amounts on the edges of the area of the thread 113 therebelow.

in accordance with one form of the present method, the screw is dipped in, or otherwise treated with, a weak acid solution to clean the thread surfaces and if necessary slightly to toughen the same. The cleaned screw is then heated to a temperature inthe range from about 500 F. to about 550 F., a preferred temperature being 525 F, and immediately thereafter mounted in the holder 151 and the powdered plastic applied thereto. in a second form of the present method, the cleaned screw has a primer coat of resin, the preferred resin being an epoxy resin, applied thereto before heating to 525 F, all as will be explained more fully hereinafter.

in a preferred example of the present method, the powdered plastic is powdered nylon 11 having a particle size to all pass through an 80 per inch mesh screen, or finer. The nylon 11 powder is placed in the hopper 155 and applied through the outlet 2% to the screw llil heated to a temperature of 525 2'2, the nylon l 1 powder being at room temperature and falling under the influence of gravity upon the selected area of the heated thread 113 while the screw lid is rotated through a predetermined angle so as to apply nylon l l to 270 of the circurnferential extent thereof. As the powdered nylon l l strikes the heated thread llfl, a portion of the nylon l l is melted and sticks to the surfaces of the thread lid, and then additional nylon l l adheres to the melted layer thereof on-the thread 113 until the desired amount of nylon ll is adhered to the thread ll?) on the screw llll. it is pointed out that at this time the nylon l l is not a cohesive single mass.

The screw lllll with the nylon ll adhered thereto is then transferred toa fusing apparatus 160, see FlG. l0, and specifically to a support plate lei thereof and within the field of a high frequency induction heating coil 162. The induction heating coil 1162, in a predetermined short time, brings the screw to a temperature sufficient to meltthe nylon 11 after which the induction heating coil M2 is shut off. The nylon ll will, when heated to its melting temperature, more or less readily flow longitudinally and circumferentially of the thread under the action of gravity to wet and to form a most intimate contact with the thread defining surfaces of the screw and will flow into any depressions in those surfaces. The melted plastic is of relatively low viscosity, as compared with plastics generally, but on cooling hardens into a coherent unitary body or plastic patch E20 extending over the crests of a predetermined number of thread convolutions.

The nylon 11 used to form the plastic patch 1.20 as described above, provides initial and reuse torques well within the values hecessary to qualify the screw i110 as a reusable self-locking screw. The nylon ll also provides good sealing under use and reuse conditions to qualify the screw llltl as a reusable self-sealing screw. in fact the screw 120 may be reused fiveor more times and still provide satisfactory selfloclting and self-sealing characteristics. The nylon ll more particularly has an inherent tendency to return to its original form after removal of the screw llll from the associated threaded member, this property being sometimes referred to as plastic memory or elastic memory, this property permitting a substantial number of reuses of the screw it ill.

Other plastics may be used in place of nylon ll but it is desirable that such other plastics have a number of properties and characteristics comparable with or similar to nylon l l, in addition to elastic memory." Thus, at its melting point the plastic should have a viscosity of the order of nylon ll and should preferably exhibit good wetting properties when in contact with metals and other surfaces. Other properties which need to be taken into consideration are relatively low moisture absorption, high resistance to abrasion, great resistance to common chemicals, high relative hardness, high strength, toughness and resiliency, and low coefficient of friction. Since for many uses, the plastic materials will be exposed to temperatures as high as 250 F., it is desirable that for general purpose uses the plastic be mechanically and chemically resistant to prolonged exposure at temperatures above 250 F.

Other considerations which enter into the selection of a plastic to be employed in accordance with the teaching of this invention are concerned, to a considerable extent, with properties facilitating manufacture of the patch type fastener. In this connection, it is desirable that the plastic be available in fine powdered form or reducible thereto, i.e., to a particle size such that all will pass an mesh screen, a large portion of the material passing a 200 mesh screen. It is also desirable that the plastic be capable of adhering directly to the material of the fastener or to another surface coating thereon with a firm bond and require no more than simple and inexpensive preparation of the metal thread surfaces to obtain such firm bond. it is also desirable that the material have a melting point or flow point which is well below the temperature at which it begins to degrade or decompose so that complex or expensive heating controls need not be required.

By way of example and illustration, other linear polyamide resins such as nylon 6, nylon 6/6, nylon 6/l0 and nylon 8 have properties as outlined above which are fairly comparable with those of nylon 11. Certain of the vinyl resins, including particularly certain vinyl chloride vinyl acetate copolymers, also possess the above described properties to an adequate degree and can be used where exposure to organic solvents would not likely be encountered. FEP fluorocarbon, a copolymer of tetrafiuoroethylcne and hexafluoro-propylene, possesses the above-described properties comparable, and in some instances superior to nylon ll and may also be used for general purpose uses. Polypropylene resins possess many of the above described properties, in comparable degree to nylon 11, and may be used where exposure to organic solvents at temperatures above 176"v F. is not likely to be encountered.

As has been pointed out above, in a second preferred method of the present invention, a primer coat of epoxy resin, or other suitable resin such as a phenolic resin, is applied to the surfaces of the screw 110 prior to the application of the plastic patch thereto. The epoxy resin utilized is a mixture in the ratio 5:2 of an epoxy resin sold under the trademark Epon and designated as resin l007-CT-and an epoxy resin sold under the trademark Beetle 227-8." The mixture of epoxy resins is dissolved and diluted in the solvent mixture containing by volume one part xylol and three parts diacetone alcohol at the ratio of live parts of solvent to one part of resin concentrate. All surfaces of the screw iii) are rendered clean, dry and free from grease, oil and other foreign matter prior to the application of the epoxy resin resolution thereto. The resin solution is applied by dipping or other suitable method at room temperature with sufficient agitation so that all surfaces of the screw llil are exposed to the solution. After the application of the resin solution, the screw llll is removed therefrom and excess solution allowed to drain off and then the screw lilil is centrifuged. The coated screw M0 is then baked at 425 F. for ten minutes to cure the epoxy resin. The resultant epoxy coating has a thickness on the order of about 0.01 mil. it is believed that the epoxy coating provides for increased and enhanced adherence between the surfaces of the thread 133 on the screw H and the plastic patch 12%.

There is illustrated in F168. it to 15 of the drawings a second embodiment of a screw made in accordance with the present invention, the screw being illustrated in R6. ll of the drawings positioned in a valve 204 the screw being designated 21b and being of the type that is both self-locking and selfsealing, and further is reusable. The valve 2% more particularly includes a valve body 231 provided with an inlet 2&2 and an oudet 263 with a valve seat 204 disposed therebetween. The screw 210 includes a shank 211 having on one end thereof a rounded closure portion 2R2 that cooperates with the valve seat 2% to restrict the flow of material from the inlet 202 to the out et 293. The other end of the screw 210 carries a tool engaging portion 213 and the portion of the shank 211 disposed between the portions 212 and 213 has a thread 214 thereon. Preferably the screw 210 has an epoxy coating 215 completely covering all surfaces thereof, the epoxy coating 215 being of the same composition and character as the epoxy coating 115: described above with respect to the screw 110.

A number of convolutions of the thread 2% carry thereon a plastic patch 220 extending completely therearound, the plastic patch 22% being a thermoplastic material formed without the application of any work-shaping forces thereto. The patch 22% as illustrated covers approximately seven convolutions of the thread 214, roughly one-quarter of the total length of the thread 214 and has a pair of circumferentially extending sides 222 having side edges 224. The boundary edge portions of the patch 22d gradually merge into the surfaces of the associated convolution of the thread 214, and in particular the side edges 224 associated with the sides 222 merge into the associated surfaces of the convolutions of the thread 2E4. The inner surface 228 of the patch 22%) conforms essentially to the outer surface of the thread 214 in the associated area thereof and is tightly bonded thereto, the epoxy coating 215 assisting in this bond, and the outer surface 229 of the patch 220 only roughly corresponds to the shape of the associated convolution; of the thread 214, see FIGS. 12 and 13, for example.

Furthermore, the side edges 224, and specifically the side edge 224 disposed toward the closure portion 212, tapers from a greater thickness toward the center of the plastic patch 220 to a very narrow thickness, thereby to reduce the stripping and shearing forces exerted by a thread of a mating threaded member during the insertion of the screw 210 thereinto. In order to provide the desired initial locking torque, as well as to provide satisfactory locking torques over a number of reuses of the screw 210, the thickness and configuration of the plastic patch 22%) is that illustrated in the drawings, FIGS. ii to 15. in general the plastic patch 220 has the configuration of the plastic patch 120 described above, and differs fundamentally in that the circumferential extent of the plastic patch 220 is a full 360.

In order to permit the plastic patch 220 to have a full 360 circumferential extent and still to preserve reasonable torque characteristics and reuse characteristics, as well as self-sealing characteristics, the plastic material forming the plastic patch 220 has been modified by adding thereto a quantity of molybdenum disulfide. More specifically, in one preferred example of the present invention, nylon l l of the same character described above with respect to H68. 1 to Ml, is provided in powdered form. There is added to the powdered nylon ll one percent of molybdenum disulfide having an average particle size less than about 1 micron. The powdered nylon 11 and the powdered molybdenum disulfide are mixed in a barrel tumbler for three hours, and the mixture thereafter applied to a heated screw 216 utilizing the apparatus and method illustrated in FIG. 7.0.

The function of the molybdenum disulfide in the completed patch 220 is not fully understood; however, it has been found that by adding the molybdenum disuli'ide in the amounts noted to the plastic patch, a full 360 patch 22% may be utilized, thereby to insure that the screw Zlui is fully self-sealing. it is believed that the molybdenum disulfide acts in the nature of a filler in the plastic material and slightly raises the modulus of elasticity thereof, and thus modifies the recoverability of the patch upon removal after use. The molybdenum disulfide is also believed to act as a nucleating agent, i.e., it permits the onset of crystallization throughout the entire plastic body substantially simultaneously and thereby prevents the growth of large spherulites from isolated nuclei, thus tending to increase the crystalinity of the patch 2.20 and also the stiffness and elastic recoverability thereof. The molybdenum disulfide also may lower the overall coefilcient expansion of the patch and thus provides increased dimensional stability thereof. Finally, it is believed that the molybdenum disulfide acts as a surface lubricant, the molybdenum disulfi de tending to rise to the outer surface 229 of the plastic patch 220 and thus to provide lubricating action in the most effective place, thus considerably reducing the tear forces applied to the plastic patch 220.

In any event, the addition from about 0.1 percent to about 5 percent of molybdenum disulfide to the plastic material permits the plastic patch 220 to have a circumferential extent of a full 360 wh le preserving both the self-locking and self-sealing characteristics thereof, even after five reuses, which structure would be entirely unsuitable for reuse in the absence of molybdenum disulfide. In this regard it is noted that if more than about 5 percent of molybdenum disulfide is added to the plastic material, the resultant plastic patch 220 is materially weakened so that tearing thereof is experienced upon reuse, and there also is a substantial loss of cohesion of the plastic patch 220. If further is pointed out that any of the other plastic materials described above with respect to the plastic patch 120 may be substituted for the nylon 11 when forming the plastic patch 220.

There is illustrated in FIGS. 16 to 20 of the drawings a third embodiment of the invention in the form of a screw 310 having a plastic patch 320 thereon, the screw 310 and the plastic patch 32 3 being of the same shape and configuration as the screw and associated plastic patch disclosed in the abovementioned US. Pat. No. 3,294,139. The screw 310 is also the type that is both self-locking and self-sealing, and further is reusable, the screw 310 including a shank 313 having on one end thereof a wrench-engaging head 312 and having formed on the shank 311 a thread 314 of standard configuration. Preferably the screw 3E0 has an epoxy coating 3?.5 completely covering all of the surfaces thereof, the epoxy coating 315 having the same composition and character as he epoxy coating described above with respect to the screw 110.

As has been stated above, the shape and form of the patch 320 is identical to that of the patch on the screw disclosed in U. S. Pat. No. 3,294,139, and more particularly includes a pair of narrow ends 321 and a pair of elongated sides 322 that are provided respectively with end edges 323 and side edges 324. The inner surface 328 of the patch 320 conforms essentially to the outer surface of the thread 314 in the associated area thereof and is tightly bonded thereto, the epoxy coating 31S assisting in this bond, and the outer surface 329 of the patch 320 only roughly corresponds to the shape of the associated convolution; of the thread 314.

The fundamental difference between the patch 320 and that disclosed in U. 8. Pat. No. 3,294,139 resides in the composition of the plastic material of the patch 320, the composition of the patch 32% being nylon 11 with the molybdenum disulfide added thereto as described above with respect to the patch 22%. it will be understood that the method of forming the patch 32% on the wrev/ 318' may be the same as that disclosed in US. Pat. No. 3,294,139, there merely being a stitut'on of the mixture of nylon l l and molybdenum for the plastic material osed in the patent. it has been found that the screw 3119 with the modified patch 320 thereon has superior operating characteristics m compared to such a screw with a like patch that does not include the molybdenum disulfide addition.

There is illustrated in FlGSQ Zlto 27 of the drawings a fourth embodiment of the invention in the form of a nut 410 having a plastic patch 420 thereon, the nut 410 being in the same shape and configuration as the nut disclosed in the above-mentioned U.S. Pat. No. 3,294,139, the nut 410 including a body lli having an opening therein and carrying an internal thread 412, wrenching flats 313 and end surfaces did and 415. The entire nut lllil is covered by an epoxy coating did having the same composition and character as the epoxy coating 1125 described above with respect to the screw lid.

A number of convolutions of the thread 412 carry thereon a plastic patch 420 of limited angular extent and limited longitudinal extent, the patch 420 having a pair of ends 421 and a pair of sides 422, the ends 421 being spaced at least one full thread convolution from the end surfaces 414 and 415, respectively. The patch 420 as illustrated covers approximately five convolutions of the thread 412, has a maximum arcuate or circumferential extent of approximately 90, and is of the shape of a free-form liquid pool; of thermoplastic material melted and fused and solidified without work-shaping pressures. The boundary edge portions of the patch 420 gradually merge into the surfaces of the associated convolutions of the thread 4-12,,and in particular the ends 421 have associated end edges 423 that gradually merge into the surfaces of the associated convolutioriof the thread 412 and the sides 422 have side edges 424 that gradually merge into the surfaces of the associated convolutions of the thread 412. The inner surface szs of the patch .420 conforms essentially to the outer surface of the thread 412 in the associated areas thereof and is tightly bonded thereto, the epoxy coating 416 assisting in this bond, and the outer surface 429 of the patch 420 only roughly corresponds to the shape of the associated convolutions of the thread 412.

Furthermore, the side edges 424 taper from a greater thickness at the center of the plastic patch 420 to a very narrow thickness at the edge thereof, and the end edges 423 likewise taper from a greater thickness at the center of the plastic patch 4120, to a very narrow thickness at the edge thereof, thereby to reduce the stripping and shearing forces exerted by the thread of a mating screw such as the screw 400 in FlG. 27 during the insertion of the screw 400 thereinto. As illustrated, the screw 400 includes a shank 401 carrying at one end a head 502 and having a thread 404 thereon shaped complementary to the thread 412, the entire screw 4l00 being illustrated as having an epoxy coating 405 thereon.

In order to provide the desired initial locking torque, as well as to provide satisfactory locking torques after a number of reuses of the nut 410, the thickness and configuration of the plastic patch 420 is that illustrated in the drawings in FlGS. 22 to 26. it will be understood that the nut 410 is self-locking, i.e., the patch 420 urges the cooperating convolutions of the threads 404i and $12 into locking engagement as illustrated in FIG. 27, but there is not necessarily any sealing between the screw 400 and the nut 410. in order to improve the desired characteristics of the nut 410, the plastic patch 420 has incorporated therein molybdenum disulfide in the same amount and for the same fundamental purposes as the patch 220 described above. it has been found that when the patch 420 has molybdenum disulfide added to the plastic material in the amount specified, there is a better balance of the frictional forces developed between the threads 404i and 412 so that an acceptable torque-tension relationship is achieved, as well as a locking torque within the prescribed limits. The addition of the molybdenum disulfide to the nylon 1 1 plastic material also seems to accentuate and enhance the abrasion resistance properties thereof. These characteristics are particularly desirable in the case wherein the threads 404 and 412 are in the fine series, the patch 420 maintaining the desired locking torque even after a number of reuses of the nut 410.

it is to be understood that changes may be made in the details and design, of construction of the self-locking threaded fasteners and the methods of making the same as described herein without departing from the true spirit and scope of the invention as set forth in the appended claims.

We claim:

l. A self-locking threaded fastener wherein the self-locking characteristic is provided by a patch of solid thermoplastic material bonded to a plurality of convolutions of the unmodified surfaces of the thread and gradumly merging at its boundary edge portions into such surfaces of the thread, said patch being formed of such thermoplastic material melted and fused and solidified without work-shaping pressures, said thermoplastic material containing from about 0.1 percent by weight to about 5 percent by weight of molybdenum disulfide.

2. The self-locking threaded fastener set forth in claim 1, wherein the patch is of the shape of a free-form liquid pool of the thermoplastic material adhered to the unmodified surfaces of the thread.

3. The self-locking threaded fastener set forth in claim 1, wherein the patch is of limited longitudinal extent to provide at least one uncoated full thread convolution between the patch and one end of the thread of the fastener.

4. The self-locking threaded fastener set forth in claim i, wherein the thermoplastic'rnaterial is selected from-the class consisting of polyamide resins, vinyl chloride-vinylacetate copolymer resins, polypropylene resins and copolymers of tetrachlorethylene and hexapropylene.

5. The self-locking threaded fastener set forth in claim 1, wherein the thermoplastic material is nylon l 1.

6. The self-locking threaded fastener set forth in claim 1, wherein the thermoplastic material contains about 1 percent by weight of molybdenum disulfide.

7. The self-locking threaded fastener set forth in claim 1, wherein the molybdenum disulfide has a particle size less than about 1 micron.

8. The self-locking threaded fastener set forth in claim 1, wherein said fastener is externally threaded and the threads thereon are of standard form.

9. The self-locking threaded fastener set forth in claim ll, wherein said fastener is internally threaded and the thread is of standard form, and the plastic patch is of limited longitudinal extent to provide at least one uncoated full thread convolution between the patch and the end of the thread of the fastener.

10. A self-locking threaded fastener wherein the selflocking characteristic is provided by a patch of solid thermoplastic material bonded to a plurality of convolutions of the unmodified surfaces of the thread and gradually merging at its boundary edge portions into such surfaces of the thread, a primer coating of synthetic organic resin material disposed between the surfaces of the thread and said patch to provide good adherence therebetween, said patch being formed of such thermoplastic material melted and fused and solidified without work-shaping pressures, said thermoplastic material containing from about 0.1 percent by weight to about 5 percent by weight of molybdenum disuliide.

ii. The self-locking threaded fastener set forth in claim 10, wherein said primer coating is essentially an epoxy resin.

12. The self-locking threaded fastener set forth in claim ill, wherein the primer coating of epoxy resin is cured by heating to a temperature in the range of from about 400 F. to about 500 F.

13. The self-locking threaded fastener set forth in claim ll, wherein the thickness of the primer coating is on the order of about 0.01 mil.

M. The self-locking threaded fastener set forth in claim 10, wherein said fastener is internally threaded and the patch is of the shape of a free-form liquid pool of the thermoplastic material.

15. An externally threaded self-locking and self-sealing fastener wherein the self-locking and self-sealing characteristics are provided by a patch of solid thermoplastic material bonded to a plurality of convolutions of the unmodified surfaces of the thread and gradually merging at its boundary edge portions into such surfaces of the thread, the circumferential extent of said patch being at least about 200said patch being formed of such thermoplastic material melted and. fused and solidified without such work-shaping pressures, said therrill moplastic material containing from about 0.1 percent by weight to about percent by weight of molybdenum disulfide.

E6. The externally threaded self-locking and self-sealing fastener set forth in claim 15, wherein the thermoplastic material contains about 1 percent by weight of molybdenum disulfide having a particle size less than about 1 micron.

17. The externally threaded self-locking and self-sealing fastener set forth in claim 15, wherein the circumferential extent of said patch is 360.

18. An externally threaded self-locking and self-sealing fastener wherein the self-locking and self-sealing characteristics are provided by a patch of solid thermoplastic material bonded to a plurality of convolutions of the unmodified surfaces of the thread and gradually merging at its boundary edge portions into such surfaces of the thread, the circumferential extent of said patch being at least about 200, a primer coating of synthetic organic resin material disposed between the surfaces of the thread and said patch to provide good adherence therebetween, said patch being formed of such thermoplastic material melted and fused and solidified without work-shaping pressures, said thermoplastic material containing from about 0.1 percent by weight to about 5 percent by weight of molybdenum disulfide.

19. The externally threaded self-locking and self-sealing fastener set forth in claim l8, wherein said primer coating is essentially an epoxy resin.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Pa 3 568 .746 Dated March 9 1971 Inventor(s) Charles C. Faroni and John S. Humphrey It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 1, line 7 "U.S.S. should be U. S.

line 8, "Preziozi" should be Preziosi line 9 after "provide" insert a method for mak lines 11 and 12, delete "a method for making". Col. 2 line 31, after "fragmentary" insert longitudina Col. 5, line 13 "an", second occurfrence should be and Col. 6 line 59 "lO07-CT" should be l007-CT-55 line 66, "resolution" should be solution Col. 8, line 32, "If" should be It Col. 10 line 73 line 75 delete "such".

Signed and sealed this 31 st day of August 1971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Acting Commissioner of Pa: 

1. A self-locking threaded fastener wherein the self-locking characteristic is provided by a patch of solid thermoplastic material bonded to a plurality of convolutions of the unmodified surfaces of the thread and gradually merging at its boundary edge portions into such surfaces of the thread, said patch being formed of such thermoplastic material melted and fused and solidified without work-shaping pressures, said thermoplastic material containing from about 0.1 percent by weight to about 5 percent by weight of molybdenum disulfide.
 2. The self-locking threaded fastener set forth in claim 1, wherein the patch is of the shape of a free-form liquid pool of the thermoplastic material adhered to the unmodified surfaces of the thread.
 3. The self-locking threaded fastener set forth in claim 1, wherein the patch is of limited longitudinal extent to provide at least one uncoated full thread convolution between the patch and one end of the thread of the fastener.
 4. The self-locking threaded fastener set forth in claim 1, wherein the thermoplastic material is selected from the class consisting of polyamide resins, vinyl chloride-vinyl acetate copolymer resins, polypropylene resins and copolymers of tetrachlorethylene and hexapropylene.
 5. The self-locking threaded fastener set forth in claim 1, wherein the thermoplastic material is nylon
 11. 6. The self-locking threaded fastener set forth in claim 1, wherein the thermoplastic material contains about 1 percent by weight of molybdenum disulfide.
 7. The self-locking threaded fastener set forth in claim 1, wherein the molybdenum disulfide has a particle size less than about 1 micron.
 8. The self-locking threaded fastener set forth in claim 1, wherein said fastener is externally threaded and the threads thereon are of standard form.
 9. The self-locking threaded fastener set forth in claim 1, wherein said fastener is internally threaded and the thread is of standard form, and the plastic patch is of limited longitudinal extent to provide at least one uncoated full thread convolution between the patch and the end of the thread of the fastener.
 10. A self-locking threaded fastener wherein the self-locking characteristic is provided by a patch of solid thermoplastic material bonded to a plurality of convolutions of the unmodified surfaces of the thread and gradually merging at its boundary edge portions into such surfaces of the thread, a primer coating of synthetic organic resin material disposed between the surfaces of the thread and said patch to provide good adherence therebetween, said patch being formed of such thermoplastic material melted and fused and solidified without work-shaping pressures, said thermoplastic material containing from about 0.1 percent by weight to about 5 percent by weight of molybdenum disulfide.
 11. The self-locking threaded fastener set forth in claim 10, wherein said primEr coating is essentially an epoxy resin.
 12. The self-locking threaded fastener set forth in claim 11, wherein the primer coating of epoxy resin is cured by heating to a temperature in the range of from about 400* F. to about 500* F.
 13. The self-locking threaded fastener set forth in claim 11, wherein the thickness of the primer coating is on the order of about 0.01 mil.
 14. The self-locking threaded fastener set forth in claim 10, wherein said fastener is internally threaded and the patch is of the shape of a free-form liquid pool of the thermoplastic material.
 15. An externally threaded self-locking and self-sealing fastener wherein the self-locking and self-sealing characteristics are provided by a patch of solid thermoplastic material bonded to a plurality of convolutions of the unmodified surfaces of the thread and gradually merging at its boundary edge portions into such surfaces of the thread, the circumferential extent of said patch being at least about 200*said patch being formed of such thermoplastic material melted and fused and solidified without such work-shaping pressures, said thermoplastic material containing from about 0.1 percent by weight to about 5 percent by weight of molybdenum disulfide.
 16. The externally threaded self-locking and self-sealing fastener set forth in claim 15, wherein the thermoplastic material contains about 1 percent by weight of molybdenum disulfide having a particle size less than about 1 micron.
 17. The externally threaded self-locking and self-sealing fastener set forth in claim 15, wherein the circumferential extent of said patch is 360*.
 18. An externally threaded self-locking and self-sealing fastener wherein the self-locking and self-sealing characteristics are provided by a patch of solid thermoplastic material bonded to a plurality of convolutions of the unmodified surfaces of the thread and gradually merging at its boundary edge portions into such surfaces of the thread, the circumferential extent of said patch being at least about 200*, a primer coating of synthetic organic resin material disposed between the surfaces of the thread and said patch to provide good adherence therebetween, said patch being formed of such thermoplastic material melted and fused and solidified without work-shaping pressures, said thermoplastic material containing from about 0.1 percent by weight to about 5 percent by weight of molybdenum disulfide.
 19. The externally threaded self-locking and self-sealing fastener set forth in claim 18, wherein said primer coating is essentially an epoxy resin. 